1. Field of the Invention
The present invention relates to formulations for flame retardant rigid polyurethane foams and is particularly concerned with improving the storage stability of the premix composition employed in the production of these foams.
Premix compositions for rigid flame retardant polyurethane foams containing chlorinated polyols, are unstable at room or elevated temperature when such premix also contains a tertiary amine catalyst. Apparently decomposition of the chlorinated polyol gives rise to HCl which forms a tertiary amine hydrochloride salt and deactivates the catalyst.
Among the objects of the present invention, accordingly, is to stabilize such premix compositions and extend the desired useful storage life thereof.
2. Prior Art
It is known to incorporate various drying oils or tall oil as such or in modified form (oxidized or hydroxylated) in polyurethane foams, as disclosed, for example, in U.S. Pat. Nos. 3,095,386 and 3,211,674.
It is also known to incorporate flame retardants into polyurethane foam formulations, among which are halogenated polyesters. According to the disclosure in U.S. Pat. No. 3,248,348, the stated difficulties of mixing such halogenated polyesters with polyisocyanates employed in polyurethane formulations, are overcome by using instead of the previous halogenated esters, hydroxylated tall oil esters which are halogenated.
It is also known to use various sulfur compounds in polyurethane formulations either for specified particular purposes or in general as included among the kinds of active hydrogen containing compounds (thiols) that can be employed to react with polyisocyanates.
U.S. Pat. Nos. 3,884,849 and 3,978,011 disclose the use of zinc salts of various carboxylic acids, including those of higher fatty acids, or zinc salts of dithiocarbamic acids as agents to prevent discoloration of large buns or slabs of low density flexible and semiflexible polyurethane foams formed from mixtures containing as flame retardants polyvinyl chloride together with zinc and antimony oxides. Also suggested for similar use are the zinc sulfide salts of benzothiazole and naphthothiazole (U.S. Pat. No. 4,018,724).